Up until the 1980s, there was dramatic growth in the creation of new surgical methods for treating a wide variety of previously untreated conditions. Over the past twenty years there has been a clear trend towards the invention of devices and methods that enable less-invasive treatment of such diseases, moving from invasive surgery, and then to less-invasive surgery, and to interventional techniques. Ultimately, it is desirable to move to totally non-invasive therapies.
Patent foramen ovale (PFO) is characterized by a persistent fetal opening between the left and right atria of the heart that allows blood to bypass the lungs. In most people, this opening permanently closes during the first few months after birth. However, a PFO is present in up to 15 percent of adults.
PFO may be associated with various heart conditions including paradoxical embolus, in which an embolus arising in venous circulation gains access to the arterial circulation through the PFO, thereby resulting in stroke or transient ischemic attack. Closure of PFO using a transcatheter approach may be medically necessary for patients with a history of cryptogenic stroke that are not candidates for anticoagulant therapy. Implantable devices, such as those of AGA Medical Corporation (Golden Valley, Minn.) and NMT Medical, Inc. (Boston, Mass.) are used to close PFOS.
It would be desirable to develop methods of treating PFO that are even less invasive than transvascular interventional techniques, thereby eliminating the need for catheters.
The following devices pertain to the use of high intensity focused ultrasound (HIFU) energy to weld the tissues of a PFO closed. Each device is used for application of energy to the tissues to be sealed. Heating of the tissues of the PFO by the HIFU causes a healing response which causes the formerly separate tissues of the PFO to heal together. In some embodiments, the energy denatures the collagen of the tissues of the different portions of the PFO, and the tissues are caused to remain in close apposition in order to allow the collagen to bond while the tissue return to normal body temperature.
By way of example, WO 99/18871 and 99/18870 to Laufer, et al. (now abandoned) describe the heating of the tissue of a PFO to induce closure through natural wound healing. These, however are invasive devices which require entering and crossing the PFO. Additionally, U.S. Pat. No. 6,562,037 to Paton et al. describes in detail methods and considerations for the rejoining of two tissue sections through the precise application of energy in a two-stage algorithm, wherein all voltage levels used are empirically derived and pre-programmed into the energy delivery control system. Again, however, all devices described would need to be in contact with the tissues to be joined. Relevant articles from the clinical literature include “High-burst-strength, feedback-controlled bipolar vessel sealing”, Kennedy et al., Surg Endosc (1998) 12:876-878. This article describes the development of a system for use in open or laparoscopic surgical procedures for achieving hemostasis in large-diameter arteries through the use of RF welding.
A wide variety of energy modes have been used to create lesions using epicardial or intracardiac probes. Radio-frequency electrical energy, microwaves, cryothermia probes, alcohol injection, laser light, and ultrasound energy are just a few of the technologies that have been pursued.
Separately, several groups have developed focused ultrasound devices with both imaging and therapeutic capabilities. These efforts began perhaps with lithotripsy, in which a high power focused ultrasound system developed by Dornier Medizintechnik, Germany, was used to break up kidney stones in the body. The kidney stones generally are located within the body at a significant depth from the skin. One ultrasound imaging system is used to aim the system at the kidney stones, and then a second, high energy ultrasound system delivers energy that breaks up the stones so they can be passed.
More recently, Therus Corp of Seattle, Wash., has developed a system to seal blood vessels after the vessels have been punctured to insert sheaths and catheters. The Therus system shrinks and seals femoral artery punctures at a depth of approximately 5 cm.
In addition, Timi-3 Systems, Inc., Santa Clara, Calif., has developed and is testing a trans-thoracic ultrasound energy delivery system to accelerate the thrombolysis process for patients suffering an acute myocardial infarction. This system delivers energy at a frequency intended to accelerate thrombolysis without damaging the myocardium or vasculature of the heart.
Epicor Medical, Inc. of Sunnyvale, Calif., has developed a localized high intensity focused ultrasound (“HIFU”) device to create lesions in the atrial walls. The Epicor device is a hand-held intraoperative surgical device, and is configured to be held directly against the epicardium or outside wall of the heart. When energized, the device creates full-thickness lesions through the atrial wall of the heart, and has demonstrated that ultrasound energy may be safely and effectively used to create atrial lesions, despite presence of blood flow past the interior wall of the atrium.
In addition, Transurgical, Inc., Setauket, N.Y. has been actively developing HIFU devices. However, while the Epicor Medical devices are placed in close approximation against the outside of the heart, the Transurgical devices are directed to intravascular catheters for heating or ablating tissue in the heart and require that the catheter be brought into close approximation with the targeted tissue.
In view of the aforementioned limitations or previously-known devices and methods, it would be desirable to provide methods and apparatus for treating PFO by heating or ablating tissue at a distance from that tissue, so that the procedure may be performed non-invasively.
It also would be desirable to provide methods and apparatus for treating PFO by applying energy from outside the body or from organs, such as the esophagus, that are easily accessible via natural body openings.